Calender strips of various materials are used for numerous applications in various industries including but not limited to the tire industry. Calender strips are used considerably in the tire industry for the production of tires. Such calender strips may be composite strips formed of a plurality of separate layers of different materials which are joined by various means before or upon passing through the calender rolls.
Calender strips used in the production of tires include body plies, tread plies and bend reinforcing material. These strips usually consist of a layer of fabric, cord material and the like bonded between inner and outer layers of an elastomeric material. These calender strips are formed by various processes, a common one of which is a dipping process in which the fabric or cord is passed through an aqueous solution containing formaldehyde and other resins which coat the fabric or cord on both sides prior to passing the coated strip through the calender rolls. The rolls press the strip into the desired configuration and smoothness and integrally bonds the fabric or cord within the elastomer. It is usually desirable that the coated layer be in the center of the resulting composite elastomer strip so that the strip is a "balanced" strip, in contrast to an "unbalanced" calender strip in which the fabric layer is separated different distances from the two opposed outer strip surfaces. However, for certain applications the calender strip may have a specified "off-balance".
It is difficult to obtain absolute accuracy in locating the fabric or cord layer within the elastomer by the primary gauging system for the calender machines. Therefore additional components are required such as beta gauges and/or other nuclear particle type systems to override and correct the primary gauging system of the calender machine to provide the most efficient means of properly locating the layer within the elastomer or coating material. A number of factors can affect the accuracy of the positioning of the fabric within the coating in addition to the calender coating roll unit. Variations in the ratio between the precalender and post-calender tension of the moving strip will effect the balance of the calender strip. Furthermore, variations in the ratio of the viscosity of the two elastomer coating layers usually due to temperature differences in the coating material, will affect the location of the fabric. These temperature differences can be caused by differences in coating roll temperatures, height or volume of the coating material supply and similar factors.
The profile of a calender strip and in particular the location of the fabric or cord layer within the strip has a continuously undulating contour both in the linear and transverse direction of the strip. In addition to the various factors described above which affect the balance of the calender strip, the fabric or cord location is constantly changing due to the constant "bumping" of the primary calender control system gauges and the periodic "bumping" of the calender roll straightening pressures. Other factors that affect the calender strip balance are imperfections in the calender rolls themselves, such as the edge to edge profile of the roll which can change throughout the roll rotation, poor runout or egg shaped rolls, and gear ratios in motor drives of the calender rolls which do not have common gear teeth multiples. Also, variations in the viscosity and/or temperature of the coating material itself has an affect on the balance of the produced calender strip.
Historically, checking balance or off-balance of the calender strip such as the body ply of a tire, has been accomplished by folding a sample strip twice and cutting it with a sharp knife and examining the cut edge visually under a magnifier. The accuracy of this existing test method is to a large degree, subjective and only provides a single instantaneous check which reflects short term variations and does not provide a continuous check over the entire running or construction of the calender strip. It also does not permit immediate adjustments of the calender rolls upon detecting of an unbalanced condition by such prior art test.
The sample strips which usually are approximately 1 inch wide by 18 inches long are just that, samples of the produced strip. These samples require a portion of the calender strip to be destroyed resulting in waste material and additional waste later on when the calendered fabric is cut for use in a tire production area, in that the portion of the finished calender strip near the location where the sample was removed must also be scrapped. Also, if it were possible to accurately read the off-balance from the folded strips, it would require many sample strips to be cut from the main calender strip to ascertain even the average balance due to the continuous changing location both in the transverse and linear direction of the fabric or cord in order to obtain an accurate reading.
Various devices and procedure have been devised for checking certain features of a composite strip containing a fabric or cord layer bonded within an elastomer strip. For example, U.S. Pat. No. 4,041,806 shows a method of dynamically checking the particular adhesion of the cord to the elastomer. U.S. Pat. No. 3,908,448 discloses a method for measuring resistance to vibration of flexible reinforced belt members. U.S. Pat. Nos. 3,659,454 and 3,871,212 disclose methods of testing characteristics of tire fabrics but not the balance of a calender fabric layer used therein. U.S. Pat. No. 3,474,666 is concerned with dynamically testing tires and industrial cords used therein by recording the stress and strain characteristics thereof by measuring the difference in rotation between two motors. However, nothing is shown or indicated in this patent for measuring the balance of a fabric layer in a calender composite strip.
U.S. Pat. No. 3,169,297 discloses an apparatus for dynamically determining the stretch or shrinkage of a continuous web by employing two current generators attached to a pair of rolls whereby movement of the rolls rotate the generators at different speeds depending upon the amount of stretching or shrinkage of the web. While this patent discloses a dynamic system that measures the difference in rotation between two rolls, the rolls do not function in the same manner nor are they used to measure the balance of a calender fabric strip as the subject invention.
U.S. Pat. No. 2,665,582 discloses another prior art apparatus for testing tire tread cord calender layers by cutting a section of tire tread in such a manner that the fabric layers extend beyond the calender rubber section and attaching loads to the ends thereof which extend over rolls so that the necessary stresses can be determined. U.S. Pat. No. 2,650,432 shows still another type of apparatus for measuring the strain of extensible materials such as fiber and various fabrics by the use of a pair of spaced wheels. The wheels pinch the strip therebetween and pull the strip in opposite directions to cause an elongation of the material which is indicated on meters connected to the two stretching rolls. The difference in rotation of the rolls is observable and therefore indicates the differentially elongation produced by the loads applied to the opposite ends of the strip. However, this patent neither discloses the measuring of the balance of a calender strip nor does it show a dynamic apparatus which indicates change in a moving calender strip as does the subject invention.
Accordingly, the need has existed for a method and apparatus for dynamically checking the balance of a fabric layer bonded within a composite calender strip which can be performed while the strip is moving and at a position closely adjacent to the calender rolls enabling nearly instantaneous adjustments to be made to the calender rolls to correct for any misalignment and bearing pressures thereof enabling necessary changes to be made to provide a calender strip in which the fabric layer is balanced therein throughout the longitudinal length as well as in its transverse cross-sectional direction.
There is no known method and apparatus for organic fabrics of which I am aware which achieves these advantages prior to my invention described below and set forth in the appended claims.